Electric ship propulsion



March 7, 1933. Q G, WATSON 1,900,594

ELECTRIC SHIP PRoPULsON Filed Sept. 7, 1929 2 Sheets-Sheet' 1 Reversing l Swibchcs l: 2 5tab oaul I Gcncvabox .5b a Placard Pan-b Mdbor'* Motor'- March 7, 1933. G, Q WATSON 1,900,594

ELECTRIC SHIP PROPULS ION ru/f-:TWOP GC01-93@ O. Watson,

H is -AtGov-ney.

Patented Mar. 7, 1933 UNITED! STATES PATENT OFFICE GEORGE O. WATSON, OF RUGBY, ENGLAND, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A' CORPORATION 0F NEW YORK f ELECTRIC SHIP PROPULSION Application led September 7, 1929, Serial No. 391,090, and in Great Britain, September 7, 1928.

My invention relates to power systems and more particularly to control gear for electric ship propulsion systems where for example a plurality of propeller shafts are driven by motors supplied with current from a lurality of generators driven by va plura ity of prime movers. v

An object of my invention is to provide an improved system of interlocking whereby a 'desired sequence of operations must beperormed inaccordance with a predetermined pattern.

Further objects of my invention will appear from a consideration of the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

According to my invention, there is provided in combination with the switching mechanism, interlockingmechanism for the switches which renders it impossible to connect the generators in parallel.

Where two propellingmotors and two generators are provided, the apparatus may comprise an isolating switch whereby one motor Acan be connected to its own generator, a second isolating switch whereby the other motor can be connected to its generator, and a tie switch which, when closed simultaneously with one of the isolating switches, serves to connect both motors to the generator associated with the isolating switch which is closed, interlocking mechanism being provided whereby when both isolating switches are free to close, the tie switch is locked open. In addition, means may be provided whereby when all the motors are connected in parallel to a single generator, the field control members are locked together so as to be incapable of separate operation. Preferably, such locking means is operated automatically by movement of the switches to connect the motors in parallel to one generator.`

f `In addition, interlocking mechanism may also be provided whereby the 4switches for connecting each motor directly to its own generator (hereinafter referred to as isolators or isolating switches) cannot be closed unless the reversing and field control meml.5,0 bers are in the oil position.V Also the revers,-

ing member and they fieldy control member l" may `beprovided whereby the field control member cannot be operated unless the reversingmember is definitely in the ahead position the astern position or the off or neutral position.

Preferably, a third member is provided for l" controlling the speed of the motor when running slowly, interlocking mechanism being provided whereby this slow speed control member `cannot be operated unless the ield control member is in a' position which will give the minimum speed setting of the governor and conversely, the iield control member cannot be moved beyond the minimum speed lwithin such range, unless the slow speed control member is in the position to give the maximum speed, which canbe obtained by means of such slow speedlever. Conveniently, the field control member serves also to regulate the loading of the governor for the turbine driving the generator which supplies power to the motor or motors.

The control member for the field is conveniently in the form of a lever provided with a latch whichiscapable of being'r'eleasedl an d disengaged, in such a way that it remains the direction of the longitudinal axis of the lever and also transversely with respect thereto. The latch is provided with biasing means tendingl Ato maintain it ina position intermeup to the stop, thus forcing the latch over to one end of its transverse travel. In addition actuating means are provided for moving the latch longitudinally with respect to the lever until itis clear of the stop, whereupon the diate the endsof itstravel, while a fixed stop l .is also `provided which cooperates with the latch, so that the lever can be moved smartly provided whereby the switches for connecting the propelling motors to the source of power cannot be closed unless the heating switchesv are in their normal running position.

My invention may be carried out in various 1 ways, but one'arrangement according thereto is illustrated diagrammatically .by way of example inthe accompanying drawings, in which: t f

' Fig. 1 isa diagrammatic representation of the electrical Acircuits of asystem inwhich interlocking mechanism according to my invention may be used.

Fig. 2 illustrates in perspective the switch operating mechanism, together with the interlocks therefor, for a system such as shown in Fig. 1y where two propelling motors and two generators are used.

, Fig. 3 shows the interlocking mechanism of Fig. 2 in the position which it occupies when the tie switch and theV port isolator are free to close, the starboard isolator being locked open. .L f y i Fig.4 shows the interlocking mechanism of Fig. 2 in the position which allows either or .both isolators to close, the tie switch being locked open.

Fig. 5 shows the interlocking mechanism'of Fig. 2 in the position which allows the tie switch and the starboard isolator to close, the port isolator being 'locked open.

Fig. 6 shows the interlocking mechanism of Fig2 in the position in which both isolators are locked open. v

Fig. 7 shows the heating switches and interlocks associated therewith.

Fig. 8 shows in further details the locking arrangementfor the doors of the heating switch cubicle.

Fig. 9 illustrates the arrangement of the control levers vand the clutch mechanism for locking together the field control Vlevers for the port and starboard `motors. y Fig. 10V shows the interlocking mechanism for the field control lever, the slow speed con-V trol .lever and the reversing lever.

v Fig. 11 illustrates the key for locking the mechanism, illustrated in Fig. 10.

Fig'. 12 illustrates a side viewof the levers c of Fig. 9 taken `along section A-A of that figure and indicates the location'of the interfrlock frame, the mechanism of which is shown in Fig. 10, and Y Fig. 13 shows a side view of the latches associated'with-the field control members shown Iin Figs. 9 and 12.

Referring to Fig. 1, the yswitchgear comd prises three switches of which the center one 1, which may be referred to as the tie switch, serves to connect both motorsr2 and 3 to one or the other of the two generators 4 and 5 when closed simultaneously with one or the other of the isolator switches 6' and 7, while the two outer switches respectively serve to connect-the port and starboard motors separately to their respective generators. These two outer switches may be referred to as the port and starboard isolators. Each of these switches is operated by a handwheel, the tie switch handwheel` being indicated at 10 in Fig. 2, while the port and starboard switch operating wheels are indicated at 11 and 12 respectively. The handwheels are secured to operating shafts or spindles 13, 14 and 15, which are connected to the switches 1, 6 and 7 through rods A16, 17 and 18. Each switch operating shaft has secured to it a locking disc19, 2O and 21. These locking discs are of the saine size and' each is provided with three notches, of which the size and angular spacing are the'same in the case of each disc. The notches in the center disc are indicated at 19a, 19?), 190, those in the port disc' at 20a, 205, 20c, while thosein the starboard disc are shown at 21a,21b,210. i

Running transversely 'across thethree rods 16, 17 and 18 are two shafts 22 and 23, one disposed above the operating shafts while the. otherV is disposed beneath them. 0n the upper transverse shaft 22 are'inounted three locking segments 24, 25 and'426, provided with notches 24a, 25a and 26a with which the discs 19,20 and 21 are respectively adapted to cooperate. The notches'24a, 25a and 26a are in alignment with one another, i. e..

their angular spacing from any given radius isV the'same for each notch. VThepiirpose of the locking` segments 24, 25 and 26 is to provide means whereby the operating shafts 13, v14 and 15 for both isolating switchesk and the tie vswitch may be 'locked either oif or on,

unlessthe field control and reversing levers are in their respective o'if positions.v To this end, the shaft 22 is provided at its left hand with a lock from which the key cannotbe,

removed unless the mechanism is in the locked condition. 'A lock such as shown in U. S. Letters Patent to J. Castell No. 1,458,520 ofJ une 12, 1923, may be used. In the pres'- ent instance,k the lock comprises a notched segment `27 having a bridge piece 28 mounted in a casing which isI not shown in the figure. The bridge piece 28 is 'fixed except as regards `.rotary motion and can only rota-te when Vthe shaft 22 has been turned to bring the notch c in the disc 27 into coincidence with the inember 28. The member 28v can ,only be turned yby means of thekey29 andthe latter is vso formed that itvcanno't 'be vremoved Y from the kcasing unless fthe bridge piece y28 has 'been 'turned in the notch so asto lock the shaft 22 iis s the shaft 22 is in the positionv in which the segments 24, 25 and 26 lock the switch operating shafts 13, 14 and 15, either in theopen position in notches 19a, 20a and 21a, or in the closed positions in notches 195, 20L and 215;

. similarly the keyy cannot be used to unlock the shaft 22 unless the lever gear is lirst locked. This arrangement renders it impossible for the isolators or forthe switch to be changed unless both the field circuits and .i ,A reversing switches are open.

' As shown in Fig. 2, the operating shafts 13, 14 and 15 are shown in the open position, but are not locked. In order'to lock them, the selector lever would have to be turned in the clockwise direction until the notch 1n segment 27 coincided with the bridge piece 28, thereby freeing the key and locking the spindles 13, 14 and 15.

The lower transverse shaft 23 serves to provide an interlock between the three operating shafts 13, 14 and 15 themselves. To this end, the shaft 23 carriesthree segments 31, 32 and 33. T he central segment 31 yis provided with two notches 31a and 315 of which the notch 31a is ot such a width that the disc y19 can pass freely through it without allowing any free movement to the segment 31. The notch 31?) on the other hand is wider, so that even when the disc 19 is in engagement with it, the segment 31 can still turn to a limited extent. The segment 32 which cooperates vwith* the locking disc 20 for the port switch operating spindle 14 is provided with .only one notch which is relativel)T wide, so as to allow free movement of` the segment 32 wlithin ylimits'when the disc 20 is in engagement with thenotch. The segment 33 which cooperates with the disc 21 is provided with a relatively wide notch 33a in a. similar manner to the segments 32.

The angular spacing of the notches 31a, 315, 32a and 33a is clearly seen from Figs. 3, 4, 5 and 6, which show the shaft 23 in four different angular positions, giving four different conditions of the interlockingmechanism. It

'will be understood that in Figs. 3, 4, 5 and 6, 'the segments are shown in vertical section, the lcorresponding cross sectional elevation being shown to the right of each vertical section.

Considering Fig. 3, it will be seen that the disc 21 is locked owing to the fact that the disc 33 is in engagement with the notch 210. The discs 19`and 2() on the other hand are free since, in the case of the former, the notch v190 is coincident with thenotch 31a while in the'case of the latter, the not-ches 20c and 32a are coincident.y Hence, with" the shaft 23'in this position, it is possible-to connect the port generator to both motors by closing the tie switch and the port'isolating switch.

In Fig. 3 there. is also shown the upper transverse shaft 22 together with its segments 24, 25 and 26 in the positions corresponding to thosey which they occupy in Fig. 2.

Turning to Fig. 4, it can be seen that with the shaft 23 in this position, the disc 19 is locked while the discs 20 and 21 are free. Hence, either or both motors can be separately connected to their respective generators by closing either or both the isolating switches. Itis not possible, however, to close t-heptie switch.V i f In Fig. 5, the disc 20 is locked while'the discs 19V and 21 are free. Hence, both motors can be connected to the starboard generator by closing the starboard isolating switch and the tie switch. The port isolating switch cannot be closed.

Lastly, Fig. 6 shows the lposition in which the discs 2O and 21 are both locked,and consequently`neither isolating switch can' be closed. Theptie switch, it is true, can be closed but will have no effect without one ofthe isolating switches. In this position, therefore, it is impossible to connect'either motor to either generator in any way whatever.

The three switches 1, 6 and 7 are mounted within cubicles and it is desirable that the doors of these should be locked before the switches are'made alive. VTo this end two locks 34 and 35, similar to the lock 27, 28 on shaft 22 are provided on the shaft 23 (see Figs. 246). These locks are operated by keys 36 and 37 respectively, of'which the key 36 also servestolock the starboard switch cubicle while the key 37 locks the port switch cubicle, the keys not being interchangeable. The

vlocks-34 and 35 are so arranged onr the shaft 23 that their keys cannot be removed unless the shaft 23 is in the position shown in Fig. 6, and the isolating switches conse uently locked in the open position. Similar y, the

locks on the cubicle doors are so arranged Y that the keys cannot be removed from them to unlock the isolating switches unless the doors themselves are locked.

A third lock 38 similar to the other two is also provided on the shaft 23 and is operated by a key 39. This same key 39 yalso serves to operate a. lock on the .door of they cubicle in which are located switches whereby a heating current may be passed through the field coils forthe purpose of keeping them dry when in port. These switches are illustrated in Fig. 7 from which it will be. seenk that each switch is provided with a cross bar 40, which will foul corresponding projections 41 onthe cubicle 4doors 42, if an attempt is made to close the latter with the switches inthe downward or field heating position. As shown in Fig. 7, the switches are in the upper position for normal running. The lock v42a for the doors 42, and Vthe lock 38 on the shaft 23 are so constructed that the common operating key 89 for both cannot be removed from either unless it is in the lockedy position. The key 39 cannot be rotated to the locked position unless the doors are closed. Hence, the heating switches must be in the normal position before the'isolating kor tie switches can be closed, and vice versa.y n f e Fig. 8 shows the locking arrangement for the doors 42. A central fixed bar 43 is provided through which an eye k44.0n the door is adapted to project when the doorf is closed.

' While the door is open, a pivoted member 45 prevents the bolt 46 from being raised, this member -being pushed out of the way against a spring 47 by the eye 44 when the door is closed. The bolt 46 can then be raised into engagement with the eye 44 to lock the door and can kbe locked in this position by means of the Castell lock 42a and the key 39. The bolt 46 is forked to engage simultaneously with the eyes in both doors. A knob i; 48 is providedfor operating the bolt.

The arrangementof the controlling levers is .shown kin Figs. 9 and 152.y vThere are six levers in all, three for the port motor and three for the starboard motor. They comprise as noted on the drawings areversing levera slow speed lever and a maneuvering lever sometimes hereinafter referred to as a fieldA lever because it controls the fields of its associated generator and motor.

The reversing levers control the reversing switches shown in Fig. 1 and have three positions, ahead, stop and' Lastern. The slow speed levers control the governor for speeds, for examplebelow one-fifth full speed that is to say, for dead slow running. A device on the turbine (not shown) ensures sufficient steam to preventthe turbine stopping or reversing dueto regeneration during maneuvering but it is up to the discretion of the a operator to speed up the turbine by this lever if reversal is called'for when running at dead slow speed. The two field levers are in the center of the group and are also used for varying the governor setting to obtain .speed variations. The first half of their vtravel is for ield switching; the remaining half of the travel being used to obtain the various speeds required on the turbine. The vertical position isythe slow speed position, correspondingtoy say one-fifth maximum turbine speed. All of these levers are interlocked as described belowin connection with Fig. 10. The interlock frame is shown to the right of the levers in the `view shown 'in Fig. 12, Fig. 10 `showing diagrammatically the arrangement of the locking bars.

When both motors are connected in parallel'to a single generator, it is necessary to' operate their field' control levers simultanelously. Therefore, means are provided. for

locking these levers together automatically` when the main switches are operated to effect the parallel connection of the motors. This automatic locking isconveniently effected by means of an electromagnetic clutch as illustrated in Fig. 9. This clutch comprises a movable member 49 adapted to slide longitudinally and having projecting-end portions 50, 51. The portion, 50 is longer than the portion 51, their relative lengths being such that by moving the member 49 over to the left in Fig. 8, the projection 51 can be made to disenE gage from the lever boss 53, while the projection 50 still remains in engagement with the lever boss 52. In order to effect the movement of the member 49 a solenoid is provided, having-a core 54 and two windings k55and 56 connected as shown to a switch 57 and a source of current. The switch 57 is mechanically connected to the tie switch in such a way that when the motors are connected in parallel the switch 57 is moved over to the left in Fig. 9, so as to energize the winding 55 and thereby move the member 49 to theright through the lever sstems shown. If, on the other hand, 1

each motor is connected separately to its own generator, the tie switch will be open and the switch 57 is moved to the right and the member 49 to the left.

Instead of a double magnet, one magnet may be used in conjunction with a spring serving to return it to its inoperative position. It is desirable that the main iield control lever which also controls the turbine governor settings should not be capable of movement beyond a minimum speed position, say onefifth full speed position unless the slow speed lever is in the position which will give the maximum speed within the slow speedrange.

Also it is necessary that the reversing lever should be incapable of movement 4unless the field lever is in the off position and, conversely, the field lever should not be capable of movement unless the reversing lever is in the off or neutral position, or definitely in one of the running positions, i. e. either ahead or astern.

In order to ensure these conditions, an interlocking mechanism as shown diagrammatically in Fig. 10 is provided. This mecha-y nism comprises a bar 58 connected to the eld control lever, a second bar 59 connected to the `slow speed lever and a l.third bar 60 yconnected `to the reversing lever yas shown in Fig. 12. Running transversely across these three bars are two lockingbars 61 andy 62, all the bars being capable of sliding movement in the d irection of vtheir length. For the sake of simplicity, the frame within whichV the bars are mounted, is not shown in the drawings.

.The bar 58 is provided with a notch 58a vadapted to engage with a projection V63 on the locking bar 61 and with a notch 585 adapted to engage with a projection 64 on the locking bar 62. The notch 585 has a length several times that of theprojection 64 in order to allow the bar 58a certain amount of free movement within predetermined limits for a purpose which will be explained later. The bar 59 is provided with a single` notch59a adapted to engage with a projection 65 on the locking bar 62 and the bar 60 has three notches 60a, 606 and 600, each adapted to engage when required, with a. projection 66 on thelocking bar 61. Themechanism as shown in Fig. 10 is in the' position which it will oc- Cupy when all the levers are in the E position. y In this'position, all the levers are free and any one of them can be moved. If, for example, it is desired to start the ship up inthe ahead direction, the reversing lever is moved into t-he ahead position, thereby moving the bar 60 until the notch 60a comes opposite the projection 66. The initial movement of the bar 60 will cause the projection 66 to ride out ofthe notch 606, thus displacing the locking barl to the left in the figureand causing the projection 63 to enter the notch 58a in the bar 58 which is connected to the field control lever. It should be noted in this connection that the projections 63 and`66 are spaced 'fas ' trol lever from the stop to the one-fifth full apart on the bar 6,1, so that when the projection 66 is clear of the notch 606, the projection 63 bears against the bottom of the notch 58a. By this means, the bar 58 and consequentlythe field leveris locked while the reversing lever is being moved from the neutral to the ahead position. As soon as the reversing lever has reached the ahead position, however, the field lever is free to move, since .the ensuing movement of the bar 58 would displace the lockingbar 61 to the right, caus- -ing lthe projection 66 `to-enter the notch "60a, thus locking the bar60 and consequently the reversing lever against movement. y.A similar result would ybe obtained if ythe reversing lever were moved into thelastern position, l i. e. until the notch 60e came ropposite the projection 66. It willfurther be noted that 'the bar 61 cannot slide to the left unless the notch 58a coincides with projection'63. This prevents movement of the Vbar.60, unless bar A58 andconsequently the field lever is in the correct position, i. e. the off position. Y Assuming that the reversing lever has bee moved into the ahead position, the `field'lever can be moved untilthe bar 58 has traveled a distance equal to the length of the notch A586,

when it would be stopped by the projection 64 engaging with the end of the notch. The projection could not ride out of 'the notch f owing to the fact that the projection 65 is bearing against the edge of the bar 59. The length of the notch 586 isequal to the travel of the bar '58 caused by moving the field conspeed' position. If it is desired to move the field 'lever beyondv the one-fifth fullY speed "position, then it is necessary to bring the slow speed lever tothe position in which the notch field lever is brought back below the one-fifth when the extension 68 has til the slot 70 coincides with the member 69,

2-6. Itrwill be appreciatedV slow speed range. VThe projection 64 canl then ride out of the notch 606, while the projection'65 enters the notch 59a and locks the slow speed lever against movement until the speed position.

' As4 already explained with reference 4to Figs. 2-6, it is desirable that the field control lever and the reversing lever shall be incapable of movement from their off positions, unless both the isolating switches are locked. To this/end, a third transverse locking bar 67 is included in the mechanism shown in Fig. and is provided with two projections 67a, 676 respectively adapted to engage with ,notches 580 and d, formed in thebars 58 and 60. The movement of bar 58 is such that notch 580 cannot coincide with projection 63. The flocking bar 67l carries an'e'xtension 68 fitted with a suitable lock comprising a saddle shaped member 69 adapted to. cooperate with a slot 70 and extension 68 (see Fig. 11)

The member 69 is mounted in a casing (not j shown) and can be turned by means of a key 29. As can be seen from the drawings, however, the member 69 can only be turned been displaced unsuchl movement of the-extension68 simultaneously causing the projections 67a and 676 to engage with their respective notches and thuslock the bars 58 Tand 60 in such aposition that the field control and reversing levers are off. The arrangement of thelock is such that the key 29cannot be removed-.unless the .member 69 is `turned ,in the notch 70, this operation,` as is evident,.serving to lock the bar ,67. in the position which it occupies when the field control and reversing leversV .areiin'their off position. y.Once thislocking operation has been accomplished, thekey 29" :can be removedl to unlock the isolating switches as described with reference to Figs. that the fsame key is usedfor locking the isolatingswitches and for locking the mechanism shown in Fig.

. 10. Hence, this key is given thesame reference numeral both in Figs. 2-6 10 and l1.

Thelocking bar 67 is only' necessary when itr isv desired to provide an interlock between the lisolating switches'fand the field and reand in 'versing levers. If such an interlock is not required, then the bar 67 may be omitted together with the lock 69, 70 and the lock 38 shown in Figs. 2-6. 4

Eachy field control lever is preferably provided with a latch which is capable of being released and disengaged in such a way that it will remain disengaged without'further attention from the operator. This latch is erate with a'quadrant 7 3. 'A second latch 71 lof usual construction with the quadrant 7 3 yin amanner :to be explained later, is also provided and cooperates.

During field switching itis desirable that v'the' maneuvering lever move over the quad- -rant 7.3 for Va predetermined distance from the stop position without encountering resistfence, but also that a pause or pauses be made zin' this movement ata predetermined point or points to allow for lfield discharges, to al- --low `the motors to' come up to speed, to allow .for synchronizing the motors, etc. In order 'to provide for such pause or pauses at'the desired Apointer points raised yprojectors are rovided on the quadrant-73 to cooperate with the latch 7.2 on the'maneuvering lever yas more Vfully ydescribed below. Only one `stop 7 3c is shown in Fig. 12. c f

In order'to render it ypossible for the opleratorjto bring the vlever smartly up to the stop 730 and leave it there with the latch disengaged, the latch member 72 is pivoted on a pin 75 carried in a fork 7 6, secured to the lever 71. The latch k72 is so mounted .onthe pin 7 5 that it Vcan slide longitudinally thereon and in order normally to maintain the pin yin the* central position, springs 77, 7 8 are provided between the member 721 andthe 'arms of -theforlr 76. The latch 71 is ladapted yto vslide 4longitudinally lina guide 79 and ican Ybe rkoperated against 1a spiing'SO by means of a handle k'81 secured to the'lever`74. VIn operation the lever L74 is movedv smartly and without hesitation VVoverlthe quadrant 7 3 until the latch 72 abuts against the stop 7 30, thereby lcompressing the spring 7 so that'the latch72 is displaced to the leftj Thelatch '72 is 'then raised above the stop 7 30 by means of aftrigger 82 so that the lspring 77 can re- -turn the latch 72 tothe'icentral'position in v 451 :which it rests on the top of the stop 7 30, leaving thelever 74 free. After the vnecessary .xpause, the lever 74 is movedl on until the vtoo'thed .portion 736 Volf the 4 quadrant is reached, with which `the latch 71-cooperates in "the ordinary way.' When moved in the opposite direction, the spring v78 -is compressed,the operation otherwise being similar. f f l vThe particular interlocks aboveV described may be associated with various electrical arrangements for controlling the 4electrical i equipment of the ship and with variousV types y of governors forc'ontrolling the speed of the ships prime movers.

Vhile vI have specifically described cer 4 tain features of construction and methods of operation, it willbe obvious to those skilled tions iarepossible and I aim, therefore, 'to

" Ycoverallsuch modifications and variations as ffall within the scope of myinvention which is defined inthe appended claims.

WhatI .claim'asV new ,and'desire to secure 'by Letters Patent vof the United States is:

1. An electric system comprising a gen-PF -erator,a motor, switch geark for connecting said :generator and said motor,fa source, of heating current for `.the fields of said motor zand said generator, switching means Vfor connecting said fields to said source of heatingrn current orto saidswitch gear, a cubicle for enclosing saidswitching means, ,a door` for said cubicle, projections on said door for pre- .venting the closure of said'door when said :locking mechanism for said switch .gear from" -which the `key cannot be withdrawn unless said switch gear for connecting .said genswitching means completes a circuit from said-B erator and motor is llocked inf-its `open position, and one key for? operating both kof said key-operatedlocking mechanisms.

Y 2. In an electric system, a vplurality of motors, a pluralityof generators, isolating Y switches for connecting each motor to its genlerator, tie :switches for connecting a plurality of 'motors to a single generator, 'field control@ 95 means for said generators andinotors, means for reversing -said motors, keyfoperated locking mechanism for said isolatingswitches and :for said tie switches from which vthe key cannot be withdrawn unless said-switches are@ locked open orclosed, key-operated locking mechanism for said vfield control means-and for said reversing kmeans from which the-key cannotbe withdrawnunless saidy field con- Y trol means Ais locked inthe 0H position andi' said reversing means is locked in the ahead,

vastern or off7 positionV and a common key for operating both `o'f'said key-operated locking mechanisms to ensure that the isolating .andtieswitch mechanisms kcannot be unlocked'l simultaneously with-the reversing means and iield control means.

c 3. In a sliip'propulsion system,

mover, a Ymain speed'control means for said prime moverarranged to control said prime? mover throughout its complete range of speed, an auxiliary' speed control means arranged for controlling the speed of-said prime mover at very slow speeds,\and means for locking said slowspeed control means untilsaid maini speed control means is in fa position which will n give the minimum speed setting for said prime mover and for locking said main speed l.control'means yagainst movement beyond its slow speed position untilsaid slowspeedcon-fl trol meansis in a position to give its'maximum speed setting for said prime mover. intheart thatfmany modifications and varia- .gjeneratorf"al kfield control'k member Vfor saidly a prime geneator and motor arranged to control also the speed of said prime mover throughout its complete range of speed, a reversing member for said motor, a W speed control member for said prime mover and interlocking c mechanism for preventing movement of said reversing lever until said field control member is in its olf position, movement of said ield control member until said reversing member is in the ahead, astern or orf position, movement of said low speed lever until said lield control member is in a position which will give its minimum speed setting and movement of said ield control member beyond its minimum speed position until said low speed control member is in a position to give its maximum speed.

5. An electric system comprising a yplurality of dynamo electric machines, switching means for connecting said machines, auxiliary switching means associated with one of said dynamo electric machines, key operated locking mechanism for said auxiliary switching means from which the key cannot be drawn unless said auxiliary switching means is locked in a predeterminedv position, key operated locking mechanism for said switching -means for connecting said dynamo electric machines from which the key cannot be withdrawn unless said switching means 1s 1n a predetermined position, and one key'for operating both of said key operated mechanisms.

In Witness whereof, I have hereunto set my hand this twenty-first day of August,

GEORGE O. WATSON. 

